Various folding knives available in the market are composed of a handle and a blade, and an end of the blade is pivotally coupled to an end of the handle, such that the blade can be rotated along its pivoting position and turned out from the handle, or turned and stored into the handle. If a user wants to use the folding knife, the user needs to hold the handle by one hand while pulling the blade by another hand to turn the blade out of the handle. However, a major drawback of this type of folding knives resides on that users have to use both hands to turn the blade out form the handle. If a user encounters a special or emergency situation and has only one hand available, then the user cannot use the folding knife to handle the emergency situation. For instance, if a diver's hand is tangled by a fish net while the diver is diving, the diver will not be able to use the folding knife to cut the fish net immediately by the other hand, and thus causing a fatal threat to the diver.
To overcome the aforementioned drawback, a design of a spring knife as shown in FIG. 1 is disclosed in U.S. Pat. No. 6,338,431. The spring knife includes a handle 20 and a blade 21, wherein the handle 20 is provided for containing the blade 21, and a lateral side of the blade 21 has a blade portion 211, and an end of the blade portion has a pivoting portion 221 pivotally coupled with an axle rod 22 that is disposed at an end of the handle 20, so that the blade 21 can be moved along the pivoting position and turned into or out from the handle 20, and the handle 20 includes a resilient element 23, and an end of the resilient element 23 is fixed to a position proximate to another end of the handle 20, and another end of the resilient element 23 is extended and fixed onto the blade 21 and at a position proximate to the pivotal connection of the handle 20 and the blade 21, such that when the blade 21 is stored completely into the handle 20, the resilient element 23 will produce a torque in a direction of turning the blade 21 into the handle 20, and the blade 21 can be stored securely into the handle 20. If a force is applied to the blade 21 to turn the blade 21 to a predetermined angle and out from the handle 20, the resilient element 23 will produce a torque to turn the blade 21 in a direction out of the handle 20, so that the blade 21 will pop out of the handle 20 automatically. In U.S. Pat. No. 6,338,431, a protruding portion 212 is protruded from a lateral side of a blade portion 211 of the blade 21 and disposed proximate to a pivotally connecting position of the handle 20 and the blade 21 to facilitate users to operate the spring knife. If the blade 21 is stored completely into the handle 20, the protruding portion 212 is passed through a lateral side of the handle 20 opposite to the blade 21 and protruded out of the handle 20, and thus the height and size of the protruding portion 212 must be designed in such a way that after a user presses the protruding portion 212, a force is exerted onto the blade 21 to turn the blade 21 out from the handle 20 with an angle equal to or greater than the predetermined angle. Therefore, the resilient element 23 can produce a torque to turn the blade 21 out from the handle 20, and the blade 21 can be popped out from the handle 20 automatically.
According to the design of the U.S. Pat. No. 6,338,431, the blade 21 on the spring knife requires a protruding portion 212 with specific height and size, but such design not only destroys the aesthetic appearance of the blade 21, but also limits the moving direction of the blade 21. Since the protruding portion 212 is passed through a lateral side of the handle 20 and situated precisely at the position where the user is holding the handle 20, therefore if the user wants to hold the handle 20 by one hand while pressing the protruding portion 212 to pop the blade 21 out from the handle 20 automatically, the user must adjust the holding angle significantly to reserve a space to facilitate the user's thumb or index finger to press the protruding portion 212. Such arrangement not only makes it difficult for the user to operate the folding knife, but also has the risk of causing accidents easily since the user cannot hold the handle 20 by one hand easily, and the spring knife may fall from the user's hand. By then, the user has only one free hand available and cannot handle the emergency situation by quickly and successfully using the spring knife.
In addition to the aforementioned functions, knife designers and manufacturers also need to take the humanistic side into consideration for the research and development to design an easy-to-operate and safe knife. Therefore, it is an important subject of the invention to design a safe and easy-to-operate spring knife.